Testing machine grip



7- F. s. BUCKINGHAM TESTING MACHINE GRIP Filed Aug. 24, 1944 INVENTORFrancs S Buckin h A TORNEY Patented Nov. 18, 1947 TESTING MACHINE GRIPFrancis S. Buckingham,

Baldwin Locomotive Works, a corporation of Pennsylvania to TheGlenolden,

Pa., assignor Application August 24, 1944, Serial No. 550,998

9 Claims. (Cl. 24-2635) This invention relates generally to materialstesting machine grips and more particularly to grips having removablegripping face inserts.

A great many attempts have heretofore been made to provide removablegripping face inserts in order to avoid recutting the gripping face on asolid block type of grip which sometimes must be completely discardedbecause of the difficulty or impossibility of reforming the face. Theproblem of providing economical and durable grips capable of repeateduse has long existed without adequate solution. In some instancesremovable inserts have been formed from strips of hardened file stock onwhich gripping teeth are out. The strips were inserted longitudinally ina main grip block and anchored at the bottom of the block to resist thetension pull of the specimen. These inserts repeatedly failed bycracking very quickly after being placed in use.

It is an object of my invention to provide an improved gripping faceinsert that reduces cracking to a minimum while still providing agripping face that is sharp, durable and economical in construction,operation and maintenance.

A further object is to provide an improved file type grip insert thatmay be easily and quickly removed from or replaced in a grip holder.

Other objects and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawing inwhich:

Fig. 1 is a fragmentary side elevation of the upper end of a testingmachine adapted to employ my improved grips;

Fig. 2 is a perspective of one half of a grip holder in which myimproved inserts are disposed;

Fig. 3 is afragmentary perspective view of the lower end of the gripholder showing a stop plate for aligning the lower ends of the gripinserts;

Fig. 4 is a partial sectional view taken on the line 4-4 of Fig. 2;

Fig, 5 is a perspective of one insert;

Fig. 6 is a fragmentary perspective showing the back surface of aninsert;

Fig. 7 is a fragmentary section of a flat face grip; and

Fig. 8 is a longitudinal section showing the inclined relation of thegrip face.

As is well-known, testing machine grips as diagrammatically indicated atl and 2 are supported in opposed crossheads 3 and4 of a materialstesting machine to grip a tension specimen 5 when the crossheads aremoved away from each other through application of a loading force by anysuitable mechanism well-known in the art. The upper and lower sets ofgrips are identical except that one set extends upwardly and the otherdownwardly, and hence the description of one will sufiice for both.Also, each set of grips is formed in right and left hand halves,otherwise identical, each consisting of a tapered block or holder 1provided with any suitable means such as gear teeth 8 for raising andlowering it within a usual tapered socket in the crossheads to separateor close the halves during insertion or removal of a specimen. Theholder as shown is provided with a V-shaped recess 9 extendinglengthwise of the holder, although this recess may have any other formto provide usual and well-known types of grip faces. Identical grippingface inserts ID are positioned in the two preferably smooth backs 9a. ofgroove 9 and each insert is provided with tapered edges H to interlockwith a complemental undercut edge l2 of the grooves. The angle of thetapered edges II' is such that the inserts at the bottom 91) of the gripV have interlocking engagement with each other over the complete surfacearea of their adjacent edges as at l3. The insert with its tapered edgesll may, of course, be used in a fiat faced grip such as diagrammaticallyindicated at M, Fig. 7. The inserts are preferably made of hardened filestock with any suitable file cuts l5 on the gripping face l5specifically shown herein as being straight across. An aligning plate Itof relatively light construction is secured to the lower end l6 of thegrip holder by screws H or other suitable means while the grip insertsare held at their upper ends by screw held removable washers l8.

To overcome the problem of excessive breakage of relatively thinelongated grip inserts ID, particularly when made of file stock which isgenerally of uniform thickness throughout its entire length from top tobottom, as in the present disclosure, I have found that instead oftrying to anchor the grip insert I0 entirely at its lowermost endsurface It as heretofore proposed with resultant crushing of such lowerend, it is possible to obtain a highly eifective grip insert byutilizing the entire back surface area 9a of the groove 9 and thelateral compression gripping force on the grip insert 10 in combinationwith a gripping type surface I 9 on the back of the insert wherebyduring gripping of the specimen the inserts ID are supported againstlengthwise movement over an extended portion of the insert and the unitstresses in the insert are correspondingly smaller by reason of beingdistributed over a wide area. To allow the lateral compression force tocause a pressure activated supporting action on surface [9, I form very:finely out teeth l9, Fig. 6, on the back surface IQ of each insert. Inactual practice I have made these cuts as fine as one hundred per inchas compared to the gripping face cuts [5 which have been as coarse asten teeth per inch. The cuts iii are preferably of criss-cross form,although other quivalent arrangements may, of course, be employed. As aresult of having teeth out in the back surface of the inserts thecompression action of the specimen on the grip face will force the teeth[9 into biting contact with the entire back surface of groove 9throughout at least that portion of its length in contact with thespecimen shank thereby providing an extraordinary holding area over asubstantial length of the gripping face instead of it being supportedsolely at its lower end 16 as heretofore. As a result of my improvedcooperative action of the compression gripping forces and utilization ofthe entire area of surface 9, the gripping faces will actually remain inposition even without the use of the aligning plate 16 whose principalfunction in my present invention is merely to align the ends of theinserts. Hence, instead of having the entire supporting force for thegrip faces localized at the lower end which has undoubtedly heretoforecaused concentrated stresses in the face with resultant breakage thereofI have distributed the holding uniformly over a large area.

It will also be noted as shown in Fig. 8 that the insert slopes inwardlytoward its upper end 20a. Preferably this slope amounts to approximatelythe depth of one tooth as measured at the lower end of the insert and asshown by the spacing from the vertical line 20'. As a result of thisarrangement, the end of the usual specimen shank will be first engagedby a few gripping teeth and as the tension load increases withconsequent wedging movement of the holders the gripping teeth willprogressively bite into the shank until finally its full length isgripped. This action is particularly helpful with hard specimen materialand it has the additional advantage of more uniformly wearing the teethalong an extended area instead of just at the end of the grip as is thecase with a true vertical face. In addition, the progressive biting inof the teeth cause pressure to be initially impressed at the upper areaof the supporting surface l9 and to be gradually expended until the fulllength of such gripping surface is in supporting engagement with theholder. It is thus seen that this inclined relation of the grip insertIf! is adapted to have a cooperative relation to the supporting orresisting teeth on the backside 19 of the insert. Any attempt to use aninclined insert with a smooth back would merely result in the insertbeing crowded and compressed at its lowermost end, although it is ofcourse apparent that my improved back supporting surface of the insertmay be used with an insert which is perfectly vertical.

My improved type of grip insert has overcome in a simple, economical andeffective manner the problem of providing a reasonably durable andsatisfactory removable gripping face insert which may be renewed atrelatively small cost whenever the specimen gripping teeth I5 becomeexcessively worn.

It will of course be understood that various changes in details ofconstruction and arrangement of parts may be made by those skilled inthe art without departing from the spirit of the invention as set forthin the appended claims.

I claim:

1. A materials grip comprising, in combination, a holder having asupporting surface extending generally in the lengthwise, direction ofpull on material being gripped, and a removable material gripping memberhaving a back surface adapted to bear against said supporting surfaceand a front side with teeth to grip the material, one of said surfaceshaving teeth adapted to be rendered operative by being laterally pressedinto biting contact with said other surface under the action of acompression gripping force exerted on the material during pullingthereof, whereby longitudinal movement of the gripping member isresisted.

2. The combination set forth in claim 1 further characterized in thatthe pressure activated resisting teeth are positioned on the backsurface of the removable gripping member and are of relatively fineformation.

3. The combination set forth in claim 1 further characterized in thatthe pressure activated resisting teeth are positioned on the backsurface of the removable gripping member and extend continuously throughthe length thereof.

4. The combination set forth in claim 1 further characterized in thatthe pressure activated resisting teeth are disposed on and extendcontinuously throughout the length and width of the removable member.

5. The combination set forth in claim 1 further characterized in thatthe removable gripping member has lengthwise edges which aretransversely tapered and the holder has a complementary recess toreceive such tapered edges.

6. The combination set forth in claim 1 further characterized in thatthe removable gripping member has lengthwise edges which aretransversely tapered and the holder has a complementary recess toreceive such tapered edges, and the angle of said tapered edges beingsuch that two gripping members may be arranged in a V-formation with theadjacent tapered edges in contact with each other over their full area.

7. The combination set forth in claim 1 further characterized in thatsaid supporting surface of the holder is relatively smooth and thegripping member is held onto said smooth surface by the pressureactivated teeth which become embedded in such surface under the lateralcompression gripping force.

8. The combination set forth in claim 1 further characterized by theprovision of an aligning member at the lower end of the removablemember, and removable means supported by the holder for engaging theupper end of the gripping member whereby the latter may be removedupwardly from the holder.

9. The combination set forth in claim 1 further characterized in thatthe gripping face of the insert is inclined inwardly toward the end of aspecimen whereby the successive gripping teeth progressively bite intothe specimen as a test load increases thereon.

FRANCIS S. BUCKINGHAM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,849,216 Adair Mar. 15, 19322,288,851 Sharp July '7, 1942 2,347,922 Nelson May 2, 1944 1,496,803Amsler June 10, 1924 1,556,094 Fletcher Oct. 6, 1925 1,559,932 BogenNov. 3, 1925

